BORON AND FLUORINE. 11 



The methyl alcohol was then twice redistilled from an all-glass 

 still (used only for this purpose) and was stored in a capped flask 

 of resistance glass. It was redistilled for each individual determi- 

 nation recorded in table 1 . A portion of 100 c.c. when evaporated 

 in platinum left no weighable residue. 



FORMIC AND HYDROFLUORIC ACIDS. (OTHER 



REAGENTS.) 



An excellent "C. P." grade of formic acid was diluted some- 

 what with water and distilled after the addition of a small quan- 

 tity of barium hydroxide. The product was redistilled with silver 

 carbonate. 



Formic acid, when distilled through glass, invariably left a 

 slight white residue upon evaporation to dryness. Even after 

 distillation from a platinum retort, a slight brownish residue 

 remained. The platinum condenser used for this purpose gave 

 excellent service in the distillation of hydrofluoric acid; formic 

 acid, however, seemed to dissolve traces of some unknown material 

 from the condenser, even after the latter had again been cleaned 

 in a variety of ways and after the acid had been redistilled several 

 times. Whether this contamination originated from impurities in 

 the platinum itself, or in the gold solder in the seams of the con- 

 denser, seemed uncertain. At any rate, as soon as the condenser in 

 question had been replaced by a seamless one of pure platinum, the 

 distillate of formic acid left no residue upon evaporation. 



After the preliminary distillations from glass the formic acid 

 was concentrated by fractionation and finally distilled from the 

 platinum apparatus just mentioned. The acid was freshly dis- 

 tilled for each determination and was stored in a platinum vessel. 



Hydrofluoric acid was purified as follows: The commercial 

 acid was treated with potassium fluoride until the filtrate gave 

 no further turbidity with pure potassium carbonate. 9 A consider- 

 able excess of potassium fluoride was then added, the clear liquid 

 decanted after standing for some time, and distilled from a lead 

 still. The product was redistilled with a little potassium per- 

 manganate and the first third of the distillate rejected. After 

 the addition of sodium phosphate the distillate was rectified 



9 As the potassium fluoride contained some silica it could not be used in this test. 

 2 



